A conventional ferroelectric thin-film solar cell is characterized in that its active layer is formed from a thin-film which is made of a single ferroelectric material, such that a built-in electrical field contributed by a ferroelectric domain wall is conducive to separation of carriers when irradiated. Although the electrical field of a ferroelectric material domain wall is stronger than the electrical field of the p-n depletion region in a conventional silicon-based solar cell, an overly low closed-circuit current density places a limit on the application of a ferroelectric material in the photovoltaic field.
Bismuth ferrite is a ferroelectric material which features an energy gap of 2.3˜2.8 eV and thus falls into the frequency range of visible light. Compared with the other ferroelectric materials with energy gaps which fall outside the frequency range of ultraviolet (UV), bismuth ferrite is suitable for use in manufacturing a ferroelectric thin-film solar cell. Basically, bismuth ferrite also features oxygen vacancies and Fe2+ defects and thus functions as a carrier capturing center whereby carriers are captured when separated by irradiation, thereby enhancing the chance of recombination. To enhance photoelectric conversion efficiency, it is feasible to change the defect concentration, the quantum conversion efficiency, and the energy gap of a ferroelectric material by element doping. However, not all types of element doping can enhance the photoelectric conversion efficiency, because the type, proportion, and preparation process of the doping element affect the current density and the photoelectric conversion efficiency of the finished products of thin-film solar cells.